Mounting Electrical Boxes


Mounting Electrical Boxes.

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Check local electrical codes for guidance concerning type and placement before installing boxes.

For convenient use, install switch boxes 44 to 48 inches above floor level, and outlet boxes 12 to 18 inches from the floor.

When using wood paneling thicker than 3/8 inch, you can screw switch and receptacle boxes directly to it. For thinner paneling, use a box with side clamps.

For clean cuts in drywall or plaster, apply masking tape around the outline of the box and score the outline with a sharp utility knife.

Whether you are upgrading the existing electrical system in your home or wiring an addition, you can find an electrical box to suit your needs. All are designed for quick and easy installation.

Electrical boxes protect connections between two or more wires or between wires and switches or fixtures.
Before buying an electrical box for a wall or ceiling, determine the type of cable it will hold. Metal boxes can be used with any type of cable; plastic boxes are designed for use with only nonmetallic-sheathed cable. You should also verify that the knockout holes and built-in connectors will accommodate the electrical cable you are using.

During construction or remodeling when wood framing is exposed, you can nail boxes directly to wall studs or ceiling joists. Some switch and outlet boxes are available with clamps or side brackets that lock onto the surrounding wall surface for situations where there is no convenient joist or stud. In order to keep the front edges of each box flush with the finished wall or ceiling surface, measure the thickness of the drywall or paneling to be installed before nailing. Allow the front edge of each box to project beyond the stud or joist by that amount.

In addition to type of cable, your choice of ceiling box also depends on the fixture it will support. For weights less than two pounds, you can use a plastic box with wing clamps that spring outward inside the ceiling cavity. You can also use a shallow metal pancake box that fastens unobtrusively to the bottom edge of a joist.

Heavier ceiling fixtures must be supported by metal boxes fastened directly to the side of a joist or suspended between joists from a sturdy metal bar.

Features of an Electrical box.

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Switch or outlet cables enter an electrical box through circular openings called knockouts (1) and are secured by built in clamps (2). Adjustable ears (3) at the top and bottom hold the box flush against wall surfaces. Removable sides (4) are fastened with locking screws and have mounting holes for nails.

Box shapes and dimensions are categorized according to their use. Switch and receptacle boxes are 2 inches wide and 3 inches high. Their depth can very from 1 1/2 to 3 1/2 inches, with 2 1/2 inches being the most common. Junction and fixture boxes are often 4 inches square and from 1 1/4 to 2 1/8 inches deep. Boxes can also be round or octagonal.

Installing Boxed in a Finished Ceiling.

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If the ceiling is inaccessible from above, cut a hole in the ceiling drywall between two joists. Extend an adjustable hanging bar between the joists. Secure the ends with screws.

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Once you determine the box location, slide the clamp fitting on the bar to tat location. Fasten the box to the fitting with the screw provided and refinish the ceiling.

Securing a box to wooden laths.

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To make the hole for the box, cut away one full lath and carefully chisel the plaster to expose one lath above and one below. Use the screw holes in the mounting ears to fasten the box to the laths.

Marking box holes.

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To speed installation of multiple boxes of the same type, you can cut a template from rigid cardboard. When tracing the box outline, omit the ears but include the side clamps if your boxes have them. Then use the template to mark the locations of the boxes on walls or ceilings.

Mounting Electrical Boxes.

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Nailing to new or unfinished work When joists or studs are accessible, you can nail or screw boxes directly to the wood. Ceiling boxes for large fixtures have flanges or hanging bars with screw holes.

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Clamping to old or existing work. To install boxes between studs or joists, you can choose from a variety of clamping devices and brackets that hold the box securely against the finished wall or ceiling.

Choosing the Right Location

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Before mounting electrical boxes in existing walls and ceilings, locate a suitable cavity between the studs or joists. To find the approximate location of studs, use a stud finder or knock on the wall and listen for a change in sound from hollow to dull. Then confirm the location by drilling test holes or a small nail. Next, make sure that the chosen location is free of obstructions. such as water pipes or air ducts. Bend an 8 inch length of wire in half to form a right angle. Insert one end of the wire through a test hole. Rotate the wire to make sure there are no obstructins. When you find a clear cavity, draw an outline of the box on the wall at that spot and then cut the opening.

Attaching Nail-in Boxes

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Ceiling Box. Align the open edge of a ceiling box with the bottom edge of an exposed joist. Drive nails into the joist through holes in the metal flanges on both sides of the box.

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Switch box. Insert two 16d nails through the holes at the back of a switch box. Before nailing, allow for the wall's thickness by extending the front of the box beyond the stud.

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Junction box. Center the back of a junction box on the vertical surface of a joist. Then secure the box with two nails or screws. Once the box is wired, screw on a metal box cover.

Using Side Brackets.

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Cut a hole in the drywall and push the box into place. Slide the long leg of a bracket upward between the box and the drywall. Then push the bracket up until its short leg fits in.

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Push the bracket down and pull it outward to anchor both legs against the back of the drywall. Bend the tabs into the box and cinch them tightly with needle-nose pliers.



Built-in Clamping Devices.

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Side Clamps. Working in combination with the ears at the front of the box, side clamps expand against the back of the wall when their screws are turned, locking the box in place.

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Flap clamps. Also operated by screws, these plastic flaps are turned horizontally to install the box and then rotated to a vertical position to grip the back of the drywall.

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Wing clamps. Found on nometallic boxes, these clamps spring outward once the box is pushed through its opening and ar tightened by turning a screw through the back of the box.

Now that you have all you need to know about installing wall outlets and switche boxes, all you have to do is pull a wire to them. I'll be going over that in a future page. Thank you for visiting my site. If you have question about a project you have or a problum with your home email me.

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